mysql: add backwards compatibility test.

Author: clutchski

tests/contrib/mysql/test_backwards_compatibility.py

@@ -0,0 +1,13 @@
+
+from ddtrace.contrib.mysql import get_traced_mysql_connection
+from tests.test_tracer import get_dummy_tracer
+from tests.contrib import config
+
+
+def test_pre_v4():
+    tracer = get_dummy_tracer()
+    MySQL = get_traced_mysql_connection(tracer, service="my-mysql-server")
+    conn = MySQL(**config.MYSQL_CONFIG)
+    cursor = conn.cursor()
+    cursor.execute("SELECT 1")
+    assert cursor.fetchone()[0] == 1